Problem: A hovercraft takes off from a platform. Its height (in meters), $x$ seconds after takeoff, is modeled by $h(x)=-(x-11)(x+3)$ How many seconds after takeoff will the hovercraft land on the ground?
Answer: The hovercraft lands on the ground when $h(x)=0$. $\begin{aligned} h(x)&=0 \\\\ -(x-11)(x+3)&=0 \\\\ \swarrow &\searrow \\\\ x-11=0\text{ or }&x+3=0 \\\\ x=11\text{ or }&x=-3 \end{aligned}$ We found that $h(x)=0$ for $x=11$ or $x=-3$. Since $x=-3$ doesn't make sense in our context, the only reasonable answer is $x=11$. In conclusion, the hovercraft will land on the ground after $11$ seconds.